Infusion pumps are medical devices that may be used to administer intravenous (IV) fluids. An infusion pump can facilitate the delivery of IV fluids while controlling the volumes and rates for the delivery of such IV fluids. The IV fluids may be delivered at continuous rates or intermittent intervals. Some infusion pumps move fluid through an IV tube using a peristaltic pumping mechanism that acts on the IV tube, while other infusion pumps rely on a cartridge or cassette-like device intended to be manipulated by a pump to cause the IV fluid to flow at the controlled rate or interval. In either case, a typical infusion pump, manipulates the IV tube or IV cartridge such that the IV fluid moves from a container to a patient. The IV tube or IV cartridge is typically connected to or integrated with an IV set (e.g., tubing, valves, and fittings for delivering fluid to a patient), and therefore the cartridge and IV set may be disposable to reduce the risk of infection and contamination.
Infusion pumps often include sensors that are used to detect gaseous air bubbles in the IV infusion fluid. Detection of such air bubbles is necessary in order to alarm a user or a clinician of a potential hazard that may cause an air embolism. In some sensing systems, the IV tube must be threaded into the pocket of the sensor to ensure the required coupling between the sensor and the IV tube is achieved. Misloading of the IV tube can occur when insufficient force is applied to insert the tubing into the sensor adequately, which can cause the tubing to move away from the sensing area and create false alarms. Furthermore, the tubing can creep over time as the force between the tubing and the sensor relaxes. This can result in an uncoupling of the sensor and the IV tube, which can also lead to false alarms. Another issue arises when air bubbles become stationary within the sensor gap due to non-optimization of the fluid flow path. This can lead to an acoustic short circuit. Additionally, IV tubing may be constructed of many different types of material. Since the sensor relies on acoustic measurements, it must be calibrated to the material used in the tubing. Moreover, because of manufacturing variations in the construction of the tubing, the material properties often vary which leads to additional non-optimization between the sensor and the tubing and again to false alarms. In other systems, such as a cassette, the air-in-line detection means is configured as a u-shaped structure that fits into an ultrasonic detector, such as shown in U.S. Pat. No. 4,842,584. These types of systems also suffer from certain deficiencies and while some improvements have been made to correct some of these deficiencies, such as those shown in U.S. Pat. No. 8,801,656, there still exists a need to further improve the sensing capacity and resistance to false alarms in these types of sensors.